Since its invention by Bimning, Quate, & Gerber in 1986, Atomic Force Microscopy (AFM) has proven to be an excellent tool for imaging a wide class of systems such as semiconductors, minerals, polymers, and biomaterials. The AFM obtains near atomic resolution by probing surfaces with micromachined cantilevers that have integrated tips. In contrast to the hand-cut aluminum foil cantilevers of the earliest AFMs, the current processes for fabricating cantilevers out of silicon or silicon nitride yield devices that are well defined and have reproducible spring constants and resonant frequencies. However, the dimensions of these devices are usually on the order of a hundred microns or more and are a limiting factor in the imaging rate and noise floor of the AFM. See: T. R. Albrecht, S. Akamine, T. E. Carver, and C. F. Quate, Microfabrication of Cantilever Styli for the Atomic Force Microscope", J. Vac. Sci. Technol., A84, 3386, July/August 1990; and O. Wolter, Th. Bayer, and J. Greschner, "Micromachined Silicon Sensors for Scanning Force Microscopy", J. Vac. Sci. Technol. B9(2), 1353, March/April 1991.
Some cantilevers have been made substantially smaller. For example, a 23-micron cantilever has been described in D. A. Walters, J. P. Cleveland, N. H. Thomson, P. K. Hansma, M. A. Wendman, G. Gurley, and V. Elings, "Short Cantilevers for Atomic Force Microscopy", Rev. Sci. Instrum. 67, 3583-3590 (1996). A 26 micron cantilever as described by D. A. Walters, M. B. Viani, G. T. Paloczi, T. E. Schaffer, J. P. Cleveland, M. Wendman, G. Gurley, V. Elings and P. K. Hansma, "Atomic Force Microscopy Using Small Cantilevers", SPIE, Proceedings Micro-Machining and Imaging 3009, 48 (1997). More recently, aluminum cantilevers as small as 9 microns have been constructed; see T. E. Schaffer, M. B. VIANI, D. A. Walters, B. Drake, E. K. Runge, J. P. Cleveland, M. Wendman, and P. K. Hansma, "An Atomic Force Microscope for Small Cantilevers", SPIE, Proceedings Micro-Machining and Imaging 3009, 48 (1997).
Various methods are known for forming tips on such cantilevers; see: H. J. Mamin, L. S. Fan, S. Hoen, D. Rugar, "Tip-based data storage using micromechanical cantilevers", Sensors and Actuators, A48, 215-219, 1995; Jan. P. Rasmussen, Peter T. Tang, Curt Sander, Ole Hansen and Per Moller, "Fabrication of an All-Metal Atomic Force Microscope Probe", Proceedings of Transducers 97, Chicago, Jun. 16-19, 1997, pg. 463; and Kirsten Ingolf Schiffmann, "Investigation of fabrication parameters for the electron-beam-induced deposition of contamination tips used in atomic force microscopy", Nanotechnology, 4, 163-169, 1993.
It is also known to deposit metal on one side of the cantilever; see Rudiger Berger, Emmanuel Delamarche, Hans Peter Lang, Christoph Gerber, James K. Gimzewski, Ernst Meyer, Hans-Joachim Guntherodt, "Surface Stress in the Self-Assembly of Alkanethiols on Gold", Science, Vol. 276, 2021, June 1997. Such a structure can have adverse properties due to bending effects as the temperature changes.
Cantilevers with dimensions on the scale of microns promise low spring constants (&lt;0.1 N/m) and high resonant frequencies (&gt;1 MHz). For example, a silicon cantilever which is 5 .mu.m long, 2 .mu.m wide, and 50 nm thick will have a calculated resonant frequency of 2.8 MHz and a spring Constance of 0.1 N/m. In contrast, the relatively large commercially available cantilevers with comparable spring constants have resonant frequencies substantially less than 100 KHz. There are several advantages to increasing the resonant frequency while maintaining the low spring constants necessary for imaging soft samples. First, higher resonant frequencies will allow for faster imaging rates. Second, cantilevers with higher resonant frequencies will have lower noise in a given bandwidth by spreading the thermal noise over a greater frequency range. Third, small cantilevers should be less affected by viscous damping, therefore, allowing increased force sensitivity.